Fields of study

The idea that distributions of dynamic savanna and grassland biomes are legacies of vegetation consumers such as fires and large mammal herbivores from ecological to evolutionary timescales is gaining acceptance. Consumers are charged with maintaining alternate grass-dominated ‘open ecosystems’ with low tree cover by actively promoting plants with traits supporting consumer persistence. The trait-driven vegetation community states according to Bond (2005) are the green, brown, and black worlds representing ability in resource competition, tolerance to fires, and tolerance to high herbivore pressure, respectively. Similarly, rapid changes in climate, human development, and human manipulation of landscapes are linked with creating open ecosystems. However, these contrasting ideas have not been robustly tested at long timescales. To achieve better interpretations of sedimentary proxy signals of vegetation trait responses to environmental drivers, I propose a two-tier analysis of black and brown worlds that considers local wetland and surrounding landscape vegetation as remaining at disequilibrium (asynchrony) in drier climates because of strong herbivore control. By contrast, equilibrium (synchrony) between local and landscape vegetation responses is likely in mesic areas or climatic phases because high moisture limits fire and herbivore activity. In this study, I revisit two key sites in South Africa’s grass-dominated ecosystems, i.e., Wonderkrater (savanna) and Tswaing Crater (grassland). I plan to extend the proxy analysis of phytoliths, charcoal, coprophilous fungal spores, and soil elemental analysis to reconstruct past vegetation responses, fire and herbivore histories, and climate/sedimentation links from ca. 15 000 -100 000 years ago. I will identify ecosystem states and their drivers based on plant functional trait responses expressed by growth-forms and physiology using pollen and phytolith-based records, with the former associated with landscape and the latter local-scale processes. Correspondence between vegetation responses to herbivory or fire at both spatial scales will be assessed especially in periods of climate change and human development in the Stone Age. Results from this study will be critical to our understanding of proxy records, biome organization, consumer-resource dynamics, and human resource-use influences on biodiversity in open ecosystems. This knowledge will be valuable for informing future biodiversity adaptation strategies to climate change and for guiding evidence-based ecosystem restoration.